Process for making electrical cut-outs



Patented Nov. 27, 1934 PATENT OFFICE PROCESS FOR MAKING ELECTRICAL CUT-OUTS Edgar A. Harty, Marblehead. Mass, assignor to General Electric Company, a corporation of New York No Drawing.

Application February 12, 1932- Serial No. 592,654

3 Claims.

The present invention relates to electrical cutouts and is more specifically concerned with a process whereby copper oxide cut-outs having predetermined definite breakdown insulation resistance may be produced.

Copper oxide cut-outs have heretofore been used in electric devices in series circuits wherein it is desirable to by-pass the current about any of the devices in case of failure thereof and there- 10 by maintain the continuity of the circuit for operation of the other devices in series therewith. For example, in lighting equipment copper oxide cut-outs have been used in order to efiectively cut out of the series circuit any lamp which has failed in operation or otherwise and thus maintain the continuity of operation of the other lamps in the circuit.

Heretofore diificulty has been experienced in so forming the copper oxide cut-outs that predetermined definite breakdown values could be obtained in the insulation. While it is known that copper can be heated in air to give an insulating layer of copper oxide thereon no satisfactory method has been developed, as far as I am aware whereby the formation of this oxide could be controlled so that a definite insulation value could be obtained and hence a cut-out of definite breakdown value.

I have discovered that by properly controlling the conditions under which the oxide is formed on the copper that I can obtain cut-outs of definite predetermined breakdown values.

In accordance with my discovery I have found that in order to control the formation of the oxide film on the copper to the desired extent and! to a point where the desired breakdown characteristics are obtained that, generally speaking, the following steps must be followed:

The copper must first be heated just below its melting point and at a temperature preferably in the neighborhood of 1000 C. The time of heating at this temperature determines the thickness of red oxide (CuzO) formed and is dependent on the heat capacity of the equipment employed.

After the initial high temperature treatment perature only for a time suflicient to give the desired breakdown value and then cooled to room temperature. It is desirable to avoid the formation of too much black oxide.

In lieu of annealing at this lower temperature, the heated metal may be gradually cooled to room temperature directly from the high temperature, the rate of cooling determining the final breakdown value of the cut-out. The faster the cooling the lower the breakdown voltage will be. The cooling to room temperature from the initial high temperature treatment is a longer procedure than that involving the use of an intermediate annealing temperature, and hence is not economically feasible in large scale production. It produces, however, as good results as are obtained with the use of the intermediate annealing temperature.

In order that the process of my invention may be more fullyunderstood and practiced by those skilled in the art to which it pertains the following examples are given, it being understood that they are purely illustrative in nature:

Emample I Formation of a copper oxide cut-out designed to break down between 200-300 volts. A copper washer diameter and .050" thick is first heated at 1010 C. for a period of 7 minutes. It is then annealed at a temperature of 150 C. for 3 /2 minutes. It is then cooled gradually, preferably overnight to room temperature.

Example II Formation of a copper oxide cut-out designed to break down between 50-150 volts. A cop-. per washer diameter and .050" thick is first heated at 1010 C, for a period of 7% minutes. It is then annealed at a temperature of 480 C. for 3 minutes. The washer is removed from the annealing furnace and after waiting 5 seconds is quenched in water. a

By means of the present invention copper oxide cut-outs of definite predetermined voltage breakdown characteristics may be easily and accurately" made.

What I claim as new and desire to secure by Letters Patent of the United States, is: a

1. A process for manufacturing copper oxide cut-outs having predetermined voltage breakdown characteristics which comprises heat treating copper metal at about 1000 C. for a definite period of time, annealing the heat-treated metal at a temperature of 150 C.-600 C. for a definite period of time and subsequently cooling the annealed metal to room temperature, the annealing temperature, the period of time of annealing, and theperiod of time o! cooling of the annealed metal to room temperature being varied in accordance with the breakdown voltage desired in 5 said cut-outs.

down voltage of the cut-out is to be relatively high or low. a

3. A process for manutacturing copper oxide cut-outs having predetermined voltage breakdown characteristics which comprises initially heat treating copper metal at a temperature in the neighborhood of, but below its melting point for a definite period of time and subsequently controlling the rate of cooling of said heat treated metal in accordance with the breakdown voltage desired in said cut-out.

EDGAR A. HAR'I'Y. 

